Pump

ABSTRACT

A pump includes a pump housing ( 10, 11, 20 ) that has a circular-cylindrical piston chamber ( 14 ), a rotatable and axially movable circular-cylindrical pump piston ( 40 ) in said chamber, means ( 30, 43 ) for rotationally driving the piston in the chamber, and means ( 11, 41; 13, 42; 67, 68 ) for imparting to the piston guided axially reciprocating movement in the piston chamber through the medium of piston rotation, wherein the pump includes lines and valve means for permitting one-way suction and one-way propulsion of pump fluid respectively into and out of the pump chambers between the ends of the piston chamber and the respective adjacent end of the piston. The means for imparting axial reciprocating movement to the piston are adapted to cause the piston to move axially at a constant speed at a constant rotational speed of the piston, at least during the expulsion of pump fluid.

[0001] The present invention relates to a pump of the kind defined inthe preamble of Claim 1.

[0002] SE-B-393441 discloses a rotationally driven circular-cylindricalpiston, which is received in a corresponding piston chamber in a pumphousing. The two end surfaces of the pump housing are mutuallysymmetrical in relation to a plane normal to the housing axis. The twoend surfaces of the piston are generally parallel with one another. Theperiphery of each end surface is shown to lie in one plane. The endsurfaces of the pump housing and the end surfaces of the piston extendobliquely to the piston axis and to tie chamber axis. The length of thepiston is such that the peripheral edges of respective end surfaces ofthe piston run concomitantly in contact with the respective periphery ofthe two end surfaces of the chamber as the piston rotates, whereby thepiston is guided to move alternately forwards and backwards as a resultof the co-action between the end surfaces of the piston and the chamber.The pump housing includes two diametrically opposed regions and hasmidway of its length pipe connectors for the supply and discharge offluid. The pump piston includes midway of its length two diametricallyopposed sides that include recesses which communicate with the inlet andthe outlet respectively. A first channel extends between one recess inthe piston to one end surface thereof. A second channel extends from theother recess of the piston to its other end surface.

[0003] It is suggested in SE-393441 that the end surfaces are slightlyconcave, such that the concave sides of respective pairs of adjacent endsurfaces of the housing and the piston will face one another.

[0004] However, the flow rate generated by the known pump is highlypulsating and is not positive throughout. Moreover, the pump has seriousdead volumes in the end positions of the piston.

[0005] Accordingly, one object of the invention is to provide a pump ofthe kind indicated above that has a smoother flow rate and a smallerdead volume at the end positions of the piston than known pumps of thiskind.

[0006] This object is achieved either fully or partially by means of thepresent invention.

[0007] The inventive pump is defined in the accompanying independentClaim 1.

[0008] Further embodiments of the invention will be apparent from theaccompanying dependent Claims.

[0009] According to the present invention, there is provided amechanical transfer curve which functions to convert rotary movement ofthe piston to a constant axial piston speed, during at least its fluiddelivery phases, and ensures that the output flow rate of the pump willbe constant at a constant speed of piston rotation.

[0010] The inventive concept encompasses several different embodiments.

[0011] In a first embodiment, the end surfaces of the piston areobliquely cut, so that the end surfaces of the piston will co-act withthe edge of respective end surfaces of the pump chambers. By specialdesign of the peripheral edge of the piston-ends and the ends of thepump chamber respectively, the axial speed of the piston will beconstant for a constant rotational speed of the piston. Both peripheraledges of the piston-ends lie continuously in contact with the endsurfaces of the pump chambers as the pump is at work.

[0012] In a second embodiment of the invention, the piston includes aperipherally extending guide groove, and the wall of the pump chamber isprovided with a guide pin which engages the guide groove. The endsurfaces of the piston and the end surfaces of the chamber are planarand perpendicular to the piston axis. By appropriate design of the guidegroove, the piston will move axially at a constant speed for a constantrotational speed. In this latter variant, the end surfaces of the pistonand the pump chambers may be designed solely with the aim of beingcomplementary in the end positions of the piston. The end surfaces ofthe piston and the pump chambers may then, e.g., be planar andperpendicular to the axis of the piston and of the pump chamber.

[0013] The pump may have in both of these variants an internal valvearrangement of the kind disclosed in SE-B-393441, for example.Alternatively, the pump chambers may have separate lines for the infeedand outfeed of the fluid concerned. These lines may include check valvesfor maintaining one-way flow of the fluid through respective lines. Thetwo outlet lines may take fluid from one source and the two outlet linesmay be combined to form a common outlet channel which delivers fluid atan essentially uniform rate of flow when the piston is rotated at aconstant speed relative to the pump chamber.

[0014] Naturally, the groove may alternatively be arranged in the wallof the pump chamber in the second variant, and the guide pin fitted onthe piston. However, it is preferred at present to provide the groove inthe piston.

[0015] In a third variant, the piston may be divided into two axiallyseparated parts which are movable relative to one another axially. Theseparts are rotated about their respective axes at a constant speed. Oneof the piston parts may be driven from a motor. The other piston partmay be driven by the first part through the medium of a coupling, suchas a splines coupling, which while providing a rotation-guided couplingbetween the piston parts enables said parts to move axially relative toone another. Extending through the cylinder wall is an outfeed portwhich, during axial displacement of the piston part, is in contact witha fluid delivery groove on the barrel surface of said piston part duringthe delivery phase of the pump. The groove has an arcuate extension ofslightly more than 180°. This provides compensation for the size of thedelivery port, so as to ensure that fluid will be delivered throughout arotational angle of 180° with respect to said piston part, wherewith thepiston part has a constant axial speed. The speed of the piston Dartconcerned is of less interest during the suction phase. Moreover,suction takes place throughout an angle that is smaller than 180°. Acomplete suction phase can be ensured whilst the pump rotates over anangle smaller than 180°, by modifying the guide groove.

[0016] Such modification of the guide groove will establish relativeaxial movement of the piston parts, which is made possible by thesplines coupling or some corresponding coupling.

[0017] Thus, in the third variant the extension of the guide groove 67will enable the piston part to move at a constant speed between its endpositions over a rotational angle of precisely 180°, whereafter thepiston is moved at a different speed through an angle smaller than 180°between the terminal positions of the piston part during a suctionphase. The two piston parts are mutually phase-shifted through 180°.

[0018] The invention will now be described by way of example withreference to the accompanying drawings.

[0019]FIG. 1 is a schematic axially sectioned view of a pump accordingto the invention.

[0020]FIG. 2 is a sectioned view taken on the line II-II in FIG. 1.

[0021]FIG. 3 is a sectioned view taken on the line III-III in FIG. 1.

[0022]FIG. 4 is an end view of one end surface of the pump piston.

[0023]FIG. 5 is a side view of the end surface shown in FIG. 4.

[0024]FIG. 6 is a schematic axially sectioned view of another embodimentof a pump according to the invention.

[0025]FIG. 7 illustrates schematically a guide groove for the piston ofthe FIG. 6 embodiment.

[0026]FIG. 8 illustrates schematically a further embodiment of aninventive pump arrangement.

[0027] The pump according to FIGS. 1-5 is based fundamentally on theconstruction according to SE-B-393441, the contents of which shall beconsidered as being incorporated in the present document.

[0028] The piston includes a piston chamber defined by a wall 10 whichhas a circular-cylindrical inner surface, and two end walls 11, 13. Thepump housing defines a chamber 14 for a piston 40 that has acircular-cylindrical outer wall, which borders closely on the barrelwall of the housing. The piston 40 can be moved axially and rotated inthe chamber 14. The piston 40 has generally parallel end surfaces 41,42, which define an angle with the plane normal to the axis of thepiston 40. The end surfaces 11, 13 are mutually mirror-symmetrical inrelation to a plane normal to the axis of a housing.

[0029] The end wall 13 of the housing is formed by a cover member 20,which is detachably connected to the housing wall 10, for instance by abayonet joint 21. The cover member 20 includes a central axiallyextending bore 22 for accommodating a corresponding drive shaft 30. Thatpart of the bore 22 which connects with the chamber 14 includes aco-axially extending and circular-cylindrical enlarged part 23 whichreceives a widened sealing-portion 31 of the shaft 30 and a blade-likeshaft portion 32 extending outwardly therefrom and a pair of projections48 from the piston, as shown more clearly in FIG. 3.

[0030] The barrel surface of the piston 40 includes two diametricallyopposed recesses 44, 45. A pump chamber 51, 52 is formed in the pumphousing, at respective ends of the piston. A channel or passageway 46extends from the recess 45 to the pump chamber 51. A channel orpassageway 47 extends from the recess 44 to the pump chamber 52.Extending from the end surface 42 of the piston is a central, blindrecess 43 for receiving the shaft part 32.

[0031] As will be seen from FIG. 3, the shaft part 32 and theprojections 48 are formed so that they will together essentially fillthe cross-sectional area of the bore 23. It will also be seen that theends of the projections 48 are terminated in a plane normal to thepiston 40, so that the bore 23 will be generally filled completely bythe illustrated components. The end wall 11 of the pump and the end 41of the piston have essentially complementary surfaces. This also appliesto the surfaces 13, 42.

[0032] As will be seen from FIG. 2, the wall 10 has two diametricallyopposed connection lines or ports 15, 16 for the infeed and outfeed offluid respectively. It will also be seen from FIG. 2 that thedisc-shaped part 49 of the piston bordering on the recesses 44, 45 havea valve function with respect to the ports or lines 15, 16.

[0033] In a preferred embodiment of the invention, the end surfaces 11,41; 42, 13 are generally complementary. Moreover, the end surfaces haveco-acting peripheries which guide axial movement of the piston and causethe piston to travel at a substantially constant speed at a constantrotational speed. One advantage in this respect is that the pumpdelivers an even fluid rate of flow.

[0034] It will be seen that during one half of a revolution, respectivechambers 51, 52 will function as a suction chamber and an expulsionchamber respectively, and will switch functions during the second halfof a revolution.

[0035]FIG. 4 is an end view of the piston-end 41 whose surface S can beconsidered to be defined by points Pn.

[0036]FIGS. 4 and 5 illustrate an orthogonal co-ordinate system wherethe Z-axis coincides with the housing axis and the piston axis. Thesurface S is tangential to the X-Y plane.

[0037] Each point Pn is defined by its angular distance α from X in theXY-plane and its radial distance α from the Z-axis and its height Zabove the XY-plane. FIG. 4 shows the channel 46. The surface S issymmetrical in relation to the X-Z plane.

[0038] Each point Pn (X, Y, Z) is defined by the relationship

[0039] Xn=a cos α

[0040] Yn=a sin α

[0041] Zn=a α h/r π

[0042] where the variable α has the limits 0<a≦r and the variable α hasthe limits −π<α≦π, wherein

[0043] r=the radius of the piston

[0044] h=the length of piston stroke

[0045] π=constant.

[0046] Each of the housing surfaces 11, 13 and the piston surfaces 41,42 have this form in the preferred embodiment.

[0047] The surface S is conveniently rounded in its plane of symmetry.The small degree of rounding required in order for acceleration of thepiston to be finite in the turning positions of the piston may beadapted between strength requirements on the one hand and the acceptanceof fluctuations in respect of the resultant fluctuations in the rate offluid flow on the other hand. The pump can be used to pump liquid or gasand has universal use. It is also suitable for pumping sensitive fluids.

[0048] The pump components can be injection-moulded with tolerances thatavoid the need for separate seals, such as O-rings and the like.

[0049]FIG. 6 illustrates an embodiment in which the barrel surface ofthe pump piston 40 includes a guide groove 67. In this embodiment, thechamber wall carries a pin 68 which engages the groove 67. The groove 67is designed to cause the piston 40 to travel axially at a constant speedbetween its end positions when the rotational speed of said piston 40 isconstant.

[0050] It will be seen that in an octagonal three-dimensionalco-ordinate system xyz, the groove 67 will follow the barrel surface ofthe piston 40 and also follow the function z=(α)−h/π

[0051]FIG. 7 shows the angle α for an arbitrary point p on the curve 67.The length of stroke of the piston, i.e. the distance with the Z-axisbetween the lowest and highest points of the groove 67 corresponds tothe length of stroke h of the piston. The ends of the piston arecomplementary with the end surfaces of the pump chamber. The dead volumeis substantially 0 at the end positions of the piston. In the case ofthe FIG. 6 embodiment, the end surfaces of the piston 40 are shown to beplanar and perpendicular to the piston axis. The end surfaces of thepump chamber are also shown to be planar and perpendicular to the axisof the pump housing.

[0052] The guide curve provides an axial cycle of piston movement witheach revolution of the piston, which is beneficial with respect to avertical arrangement of the kind shown in FIG. 1, although it will beunderstood that the curve can be modified so as to provide two or morepiston movement cycles with each revolution when so permitted by thechosen valve arrangement.

[0053] In the embodiments shown in FIGS. 1-7, the valve function isformed by connection of the inlet and outlet ports or lines 15, 16 withaxially extending piston recesses 44, 45 which widen circumferentially,where each widening is slightly smaller than one-half turn around thepiston circumference, wherewith the fluid suction and fluid deliveryphases are of equal length. There is a risk of irregularities in therate of flow of the fluid at the end positions of the piston, becausethe ports 15, 16 that connect with the recesses 44, 45 have a peripheralextension.

[0054] In a further development of the embodiment with a guide pinmounted on the cylinder wall and engaging in a guide groove in theperipheral surface of the piston (or vice versa), the piston is dividedaxially into two parts 40, 40′ which are coupled via a spline-coupling81, 82, i.e. a rotationally rigid joint which couples together thepiston parts 40, 40′ while enabling said parts to move axially inrelation to one another. The piston part 40′ is rotationally driven viaa spline-connection 32, 33 from an axially driven shaft 30 which rotatesat a constant speed.

[0055] Each piston part 40 has a circumferentially extending guidegroove 67 in which a pin 68 engages. The groove 67 has the form shown inFIG. 7 and extends through, or contains, an angle somewhat greater than180°. The pump also includes an outfeed port or line 16, 16′ whichco-acts with a peripheral groove 145, 145′ which widens over aperipheral angle that is slightly greater than 180°. As a result of thiswidening of the port 16, 16′, fluid can be pumped out during rotation ofrespective piston parts 40, 40′ through an angle of exactly 180°,wherewith said fluid is transported from respective chambers 51, 52 viaa channel 146, 146′ and via the groove 145, 145′ to the port 16, 16′ andthrough check valves 19 arranged therein. Between the fluid deliveryphases, the pin 68, 68′ moves around the groove 67, 67′ through an anglesmaller than 180°, wherein the piston 40, 40′ has corresponding suctiongrooves 144, 144′ which are then held in alignment with the suctionports 15, 15′. The suction grooves 144, 144′ are in contact withrespective pump chambers 51, 52 via channels 147, 147′ in the piston 40,40′. The suction lines connecting with the ports 15, 15′ may alsoinclude check valves 19, as shown in FIG. 8.

[0056] Because the groove 67 has a steeper rise in the part thatcorresponds to the suction groove 144, it is ensured that the pistonwill be displaced between the end positions despite the groove 144extending through an angle of less than 180°, wherewith the speeds ofthe piston parts 40, 40′, however, will be different during the suctionphase and the delivery phase respectively. These different speeds resultin relative axial movements between the piston parts 40, 40′, permittedby the coupling 81, 82. The length of the pump housing is suitablychosen to ensure that the volumes of the chambers 51, 52 will begenerally equal to 0 in the end positions of the piston.

[0057] The two piston parts are conveniently phase-shifted through 180°with respect to their fluid delivery phases, so that their commonoutflow will be constant.

1. A pump comprising a pump housing (10, 11, 20), that includes acircular-cylindrical piston chamber (14), a circular-cylindrical pumppiston (40) which is rotatable and axially displaceable in the chamber,means (30, 43) for rotationally driving the piston in the chamber, andmeans (11, 41; 13, 42; 67, 68) for imparting to the piston guided axialreciprocating movement in the piston chamber through the medium ofpiston rotation, wherein the pump includes lines and valve means forenabling pump fluid to be sucked into and pumped out of the pumpchambers in one single direction between the ends of the piston chamberand a respective closely adjacent end of the piston, characterised inthat the means for imparting axial reciprocating movement to the pistonare adapted to cause the piston to travel axially at a constant speed ata constant piston rotating speed, at least during delivery of pumpfluid.
 2. A pump according to claim 1, characterised in that themutually adjacent end surfaces (11, 41; 13, 42) of the piston and thepiston chamber respectively, said adjacent end surfaces defining pumpchambers (51, 52) with the cylindrical inner wall (10) of the pistonchamber, are generally complementary so as to minimise the dead volumeof said pump chambers (51, 52).
 3. A pump according to claim 2,characterised in that each of the end surfaces is defined by points PnQ(n, Yn, Zn) in a three-dimensional orthogonal co-ordinate system X, Y,Z, wherein Z lies in the chamber axis and the piston axis, and whereinthe end surface is tangential to the XY-plane of the system Xn=a cos αYn=a sin α Zn=a α h/r π where the variable α denotes the radial distanceof the point from the Z-axis, and the variable α denotes the angulardistance of the point from the XZ-plane about Z 0<a≦r −π<α≦π, whereinr=the radius of the piston h=the length of piston stroke π=constant. 4.A pump according to claim 1 or 2, characterised in that the barrel wallof the piston (40) or of the chamber (14) includes a guide groove (67);in that the barrel wall of the chamber or of the piston (40) carries aguide pin (68) that engages in the groove (87); and in that the groove(67) is designed to cause the piston to move axially at a constant speedbetween its end positions at a constant rotational speed of the piston.5. A pump according to any one of claims 1-4, characterised in that adrive shaft (30) co-axial with the piston extends along a channel (22,23) through a housing wall (20) and has a non-round dogging part (32)which engages in a dogging opening (43) in the adjacent end of thepiston (40); in that the channel (22, 23) has adjacent the piston awidened part which receives a longitudinal section of the non-rounddogging part on the one hand and filling bodies (48) disposed on thepiston on the other hand, wherein the dogging part (32) and the fillingbodies (48) fill the cross-sectional area of the widened part (23).
 6. Apump according to any one of claims 2-5, characterised in that the shaft(30) has a widened part (31) which fills an axially outer part of thewidened portion (23) of the channel; in that the filling bodies (48) areterminated in a plane normal to the axis of the piston (40) and fill theremaining part of the widened portion of the channel together with thedogging part (32) when the adjacent pump chamber (52) has a minimisedvolume.
 7. A pump according to any one of claims 4-6, characterised inthat the piston (40) has rotationally symmetrical ends.
 8. A pumpaccording to claim 7, characterised in that the ends of the piston andof the pump chambers are generally planar and perpendicular to the axisof the piston.
 9. A pump according to any one of claims 1-8,characterised by an inlet port or line (15) and an outlet port or line(16) which connect through the pump chamber wall (10) in twodiametrically opposed regions of the piston chamber (14) in alongitudinal centre region thereof, two diametrically opposed recessesor cavities (44, 45) in the longitudinal centre region of the piston, afirst channel (46) in the piston between its latter recess (45) and itsone end surface (41), a second channel (47) in the piston between itssecond recess (44) and its second end surface (42).
 10. A pump accordingto any one of claims 1, 2, 4-8, characterised in that the piston isdivided into two axially separated parts (40, 40′); in that each of saidpiston parts has an own device (67, 68; 67′, 68′) for translatingrotational speed to axial movement speed; in that each piston part has afirst groove (144, 144′) which is in contact with a fluid inlet port(15, 15′) and has a peripheral widening of less than 180°; in that eachpiston part has a second groove (145) which is in contact with an outletport (16, 16′) and which has a peripheral widening of more than 180°, sothat fluid will be delivered through a rotational angle of 180°; in thatthe guide groove (67) is adapted to cause the piston to move at aconstant axial speed during the pump delivery phase at a constant speedof piston rotation; and in that the piston parts (40, 40′) are adaptedto be rotationally driven at a constant and similar speed of rotationand are adapted for axial movement in relation to each other.